2 . LED provides almost mono chromatics light . This suitable for small distance transmission . It is infact , a low cost device as compared to diode lasers .
Line Communication
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Transmission lines are used to interconnect points separated from each other . For example interconnection between a transmitter and a receiver or a transmitter and antenna or an antenna and a receiver are achieved through transmission lines . Line communication may be in the form of electrical signal or optical signal .
Optical Fibres
An optical fibre is a long thread consisting of a central core of glass or plastic of uniform refractive index . It is surrounded by a cladding of material of refractive index less than that of the core and a protective Jacket of insulating material .
There are three types of optical fibre configuration
1 . Single mode step index fibre 2 . Multi mode step index fibre 3 . Multi mode graded index fibre .
Applications of Optical Fibres
1 . A bundle of optical fibres is called light pipe . This pipe can transmit as image . Since the pipe is flexible , it can be twisted in any desired manner . Hence it is used medical and optical examination of even the inaccessible parts of human body , e . g ., in endoscopy .
2 . Optical fibres are used in transmission and reception of electrical signals by converting them first into light signals .